Britain's technology managers have issued a warning about spam e-mails that act as a new way for Windows viruses to penetrate organisations.

The spam message tricks people into clicking on a link that takes them to a website but also, unseen, delivers a virus too.

Versions of the virus-bearing spam let people unsubscribe from bogus newsletters or claim to give away electronic greetings cards.

Technology managers fear that the viruses delivered by the malicious message will include key logging programs that will steal login details, passwords or credit card numbers.

Hidden and dangerous

Before now senders of unwanted commercial e-mail have used viruses to gain control of innocent machines that they use to send millions of messages on their behalf.

But now in a reversal of this tactic, virus writers are adopting the tactics of spammers to spread their own malicious creations.

A warning about these spam-viruses was released by the Corporate IT Forum (Tif), which is the industry association for senior technology managers working at more than 130 of Britain's largest organisations.

Over the past few years many companies have got used to tackling viruses because of a surge in the numbers of malicious programs circulating via e-mail.

Spam is becoming a big problem too and is often hard to filter out because it can resemble legitimate e-mail messages.

By putting links to websites that download viruses, the creators of the viruses are avoiding the scanners and filters that stop malicious programs that typically travel inside e-mails.

'Danger of spam'

"Clicking on a link in a spam e-mail is the equivalent of handing a burglar the keys to your house," said David Roberts, chief executive of Tif.

"People must understand that there could be a very nasty shock lurking behind each and every spam e-mail."

Mr Roberts said spam was becoming an increasingly large problem and 80% of the e-mail dealt with by some Tif members was now unwanted commercial messages.

He said the rise of the spam-virus turned what was an irritant into something more dangerous.

Mr Roberts urged people to think before they click on links in e-mail messages and to be suspicious of any messages they get that they were not expecting.